Eighty percent of the world energy demand is currently being met by fossil fuels. However, two major problems exist with the continued use of fossil fuels. First, fossil fuels are not available in unlimited quantities and will eventually be depleted. Second, fossil fuels cause serious environmental problems such as climate changes, melting of icecaps, global warming, acid rain, rising sea levels, pollution, oil spills, and ozone layer depletion, to name a few. In order to reduce dependence on fossil fuels and decrease the pollution created by fossil fuels, alternative solutions have been developed such as the creation of fuel cells.
Fuel cells have the potential to become an important energy conversion technology. Several types of fuel cells exist such as, for example, solid polymer electrolyte fuel cells, phosphoric acid fuel cells, alkaline fuel cells, molten carbonate fuel cells, and solid oxide fuel cells. The solid polymer electrolyte fuel cells are being developed for transport applications as well as for stationary fuel cell applications and portable fuel cell applications. The key features of this type of fuel cell include lower temperature/pressure ranges and a polymer electrolyte membrane. The solid polymer electrolyte fuel cells employ a solid polymer electrolyte to separate the fuel from the oxidant. The chemical energy liberated during the electrochemical reaction of hydrogen and oxygen is transformed to electrical energy. Desired characteristics for polymer membrane electrolyte materials used for SPEFCs include 1) high proton conductivity, 2) low electronic conductivity, 3) low permeability to fuel and oxidant, 4) low water transport through diffusion and electro-osmosis, 5) oxidative and hydrolytic stability, 6) good mechanical properties in both the dry and hydrated states, 7) low cost, and 8) capability for fabrication into membrane electrode assemblies (MEAs).
In SPEFCs, the so-called proton-conducting (exchange) membranes normally use carbon-fluorine backbone chains with perfluoro side chains containing sulfonic acid groups, such as Nafion, the first of a class of synthetic polymers with ionic properties discovered by DuPont, or other perfluorinated electrolyte membranes, such as Flemion™ from Asashi Glass Co., Ltd (Japan). Currently, almost all of the existing membrane materials for SPEFCs depend on absorbed water and its interaction with acid groups to produce protonic conductivity. Water management can be very difficult with SPEFCs because water in the membrane is attracted toward the cathode of the cell through polarization. Too much water will flood the membrane and too little water will dry the membrane and, in both cases, power output will drop. Therefore, water management is crucial to the performance of PEMFCs. In addition, the membrane is sensitive to things like metal ions, which can be introduced by corrosion of metallic bipolar plates, metallic components in the fuel cell system, or from contaminants in the fuel/oxidant. Both water transport and mechanical properties are key issues with existing SPEFCs. Accordingly, there is a need for a water independent membrane with high protonic conductivity for use as a solid electrolyte in solid polymer electrolyte fuel cells, such as proton selective membranes (PSMs).